1. Field of the Invention
The present invention relates to optical beam expanded beam connectors, in particular ferrule assemblies in expanded beam connectors.
2. Description of Related Art
There are many advantages of transmitting light signal via optical fiber waveguides and the use thereof is diverse. Single or multiple fiber waveguides may be used simply for transmitting visible light to a remote location. Complex telephony and data communication systems may transmit digitized data through optical signals within the waveguides. These applications couple fibers in an end-to-end relationship, with the coupling being one source of light loss. Precision alignment of two polished ends of fibers is needed to ensure that optical loss in a fiber link is less than the specified optical loss budget for a system. For single-mode telecommunication-grade fiber, this typically corresponds to connector fiber alignment tolerances that are less than 1000 nm. This means that in both parallel fiber and single fiber links, operating at multi-gigabit rates, the components applied to align the fibers must be assembled and fabricated with sub-micron precision.
In an optical fiber connection, an optical fiber connector terminates the end of a cable that contains one or multiple fibers, and enables quicker connection and disconnection as compared to splicing. The connectors mechanically couple and align the cores of fibers so that light can pass end-to-end. The end of an optical fiber is supported in a ferrule, with an end face of the optical fiber positioned generally flush with or slightly protruding from an end face of the ferrule. When complementary ferrules in connector assemblies are mated, the optical fiber of one ferrule is aligned with a mating optical fiber of the other ferrule. Better connectors lose very little light due to reflection or misalignment of the fibers. Connectors, in both parallel/multiple fiber and single fiber links, operating at multi-gigabit rates must be assembled with subcomponents fabricated with sub micron precision. As if producing parts with such precision levels were not challenging enough, for the resulting end products to be economical it must be done in an automated, high-speed process.
In some applications, the end faces of mating optical fibers physically contact one another to effect signal transmission between the mating optical fiber pair. In such applications, various factors may reduce the efficiency of light transmission between the optical fiber pair, such as irregularities, burrs or scratches in the fiber end faces, misalignment of the optical fiber pair, as well as dust or debris between the optical fibers at the mating interface. Due to the small optical path relative to the size of any foreign objects such as dust or debris, any such foreign objects will interfere with the transmission of light.
Heretofore, prior art expanded beam connectors have been developed to expand the size of the optical beam and transmit the beam through an air gap between the connectors. By expanding the beam, the relative size difference between the dust or debris and the beam is increased which thus reduces the impact of any dust or debris as well as any misalignment on the efficiency of the light transmission. As a result, expanded beam optical fiber connectors are often preferable in relatively dirty and high vibration environments.
Heretofore, prior art expanded beam connectors include a lens mounted adjacent an end face of each optical fiber. Two types of lenses are commonly used—collimating and cross-focusing. A collimating lens receives light output from a first optical fiber and expands the beam to a relatively large diameter. When using a collimating lens, a second lens and ferrule assembly is similarly configured with a collimating lens positioned adjacent the end face of a second optical fiber for receiving the expanded beam, and refocuses the beam at the input end face of the second optical fiber. A cross-focusing lens receives the light from a first optical fiber, expands it to a relatively large diameter and then focuses the light from the relatively large diameter at a specific focal point. With cross-focusing lenses, the lens and ferrule assembly may be mated with either another lens and ferrule assembly having a cross-focusing lens or with a non-lensed ferrule assembly as is known in the art.
Currently, it is generally accepted that prior art optical fiber connectors cost too much to manufacture and the reliability and loss characteristics are more to be desired. The lens in an expanded beam connector is an additional component, which is required to be optically coupled to the end face of the optical fiber in an assembly, thus requiring additional component costs and additional manufacturing costs. Prior art expanded beam connectors still result in relatively high insertion losses and return losses.
The costs of producing optical fiber connectors must decrease if fiber optics is to be the communication media of choice for short haul and very short reach applications. The relatively widespread and ever increasing utilization of optical fibers in communication systems, data processing and other signal transmission systems has created a demand for satisfactory and efficient means of inter-connecting terminated optical fiber terminals.
It is therefore desirable to develop an improved optical fiber expanded beam connector, which has low insertion loss and low return loss, and which can be fabricated in high throughput and at low costs.